1. Field of the Invention
This invention relates to sewing machines having stitch forming mechanism which may be controlled to produce a succession of different ornamental stitch configurations together defining a stitch pattern and, more particularly, to sewing machines capable of producting such stitch patterns as honeycomb patterns or buttonhole stitch patterns in which accuracy of control of the different stitch configurations defining the stitch pattern critically influences the appearance of the pattern.
2. Description of the Prior Art
This invention, as applied to the four-step buttonhole mechanism of a sewing machine, is an improvement of the U.S. Pat. No. 4,553,491 of R. B. Brauch et al, Nov. 19, 1985, which discloses the closest prior art of which we are aware.
In the U.S. Pat. No. 4,553,491, the density of zigzag stitching along the opposite sides of the buttonhole is influenced by rendering effective forward or reverse feed cams, respectively, from the barring stitch forming condition controlled by a barring stitch feed cam. Since the buttonhole side stitches are arranged laterally opposite each other, even slight differences in density therebetween are noticeable. Using the mechanism disclosed in U.S. Pat. No. 4,553,491, a noticeable variation in buttonhole side stitch density can be obtained. This invention relates to the recognition of the cause of such variation, and novel and effective measures for obviating it.